The present invention is directed to various magnetohydrodynamic applications. In one aspect, a magnetohydrodynamic fluid transducer is contemplated for sensing perturbations in a electrically conducted fluid. The transducer uses not only a magnetohydrodynamic sensor, but also a fluid displacement sensor, such as a strain gauge, to measure the perturbation in a fluid. This has significant advantages in sensing acceleration rates, and from that the velocity and displacement of a body. In a second aspect, the techniques can be employed for power generation at ambient temperatures from the flow of an electrically conductive fluid, such as seawater.
One example of the employment of a magnetohydrodynamic sensing device would be in seismology. In the prior art, a variety of seismological sensing apparatus have been proposed for monitoring various forms of disturbances or shock waves. The shock waves may be generated in response to earthquakes, tests of nuclear warheads, or from other conventional sources such as the hydraulic vibrators or conventional explosions employed in the oil industry to locate subsurface oil deposits. When an earthquake occurs, a sudden release of accumulated strain results in the propagation of a number of different types of seismological waves. Geophones have previously been employed to measure various parameters associated with earthquakes, such as the velocity of subsurface movement of waves, the rate of change of velocity, and the duration of the event. Shear waves, or S-waves, are the primary signal generated by an earthquake. When an extreme disturbance occurs in a homogeneous environment, a spherical front is generated, and a P-wave results. Such a wave is characterized by alternating compression and rarefaction through the subsurface of the earth, somewhat similar to the structure of sound waves in air. Nuclear blasts in conjunction with underground tests primarily radiate P-waves.
At the interface of the earth with air, Rayleigh waves are generated. Such waves are associated with both earthquakes and underground nuclear tests. Love waves are generated primarily from earthquakes, and are 10 generally transverse to the direction of travel of Rayleigh waves. A wide variety of other complex wave forms resulting from reflection and refraction effects are also known in seismology. A useful discussion of waves, along with recitation of the possibility of monitoring such waves for purposes of policing a total test ban treaty is discussed in Scientific American, Vol. 247, No. 4, pages 47-57, October, 1982.
In the prior art, a variety of geophones and/or seismometers have been proposed. Essentially known prior art devices include a rigid, generally conically shaped outer casing or enclosure housing an internal element of some form for sensing vibration. A variety of different sensors and/or transducers have been proposed to originate an electrical signal corresponding to seismological vibration. For example, Hayes in U.S. Pat. No. 1,980,993, discloses a sealed chamber in which pneumatic pressure results in the generation of an electrical signal in response to seismological vibration. Bound in U.S. Pat. No. 3,806,909 employs an internal piezoelectric element sensitive to soil stresses for generating a seismological responsive signal. Massa in U.S. Pat. No. 3,360,772 proposes a geophone in which a bilaminar piezoelectric element is suspended across an interior within the geophone housing for sensing vibrations and producing a proportional electrical signal.
The seismometer proposed by Baltosser in U.S. Pat. No. 2,748,370 contemplates the use of an electromagnetic sensor system interiorly of the casing for producing vibration sensing. Ording in U.S. Pat. Nos. 2,712,124 and 2,759,552 also discloses electromagnetic means for generating a proportional electrical signal. Sanderson in U.S. Pat. No. 2,677,270 senses vibration in response to the differential conductivity within a fluid medium as a gaseous bubble confined within a fluid chamber moves 10 about in response to sudden seismological vibration. Other than less relevant art known to me includes U.S. Pat. Nos. 2,683,867 and 3,474,405.
Seismological sensing technology relates generally to the broader science of perturbation monitoring. Physically shock resistant but sensitive motion sensors somewhat similar to a geophone are of necessity in a wide variety of applications. Thus, velocity meters, accelerometers, and servo motion sensors commonly find usage within geophones, impact gauges, stethoscopes, inertial sensors, inertial guidance systems, vibration measuring systems, hydrophonic sensing instrumentation and the like.
A basic magnetohydrodynamic sensor embodies the capability of being useful in the three major modes of motion sensing (those being displacement meter, velocity meter, and accelerometer), either by direct transducer design or by servo design.
Displacement meters are motion sensors whose natural period of vibration is larger than the period of frequency of perturbation being measured. Such instruments indicate the actual linear displacement magnitude of the perturbation. Velocity meters are motion sensors whose signal output in response to perturbations is in direct proportion to the perturbation behavior characteristics. Such instruments indicate the velocity of the motion being measured. Accelerometers are motion sensors which normally have natural periods of vibration which are shorter in duration than the frequency of incoming perturbations. Such sensors produce signal logic capable of measuring the acceleration of incoming measured perturbations. Velocity meters may be converted into accelerometers by the use of well known differentiator circuits. In the practice of seismology, an earthquake measuring instrumentation platform will commonly have all three types of motion sensors in use so that displacement, velocity, and acceleration can be logged concurrently.
Servo-motion sensors are designed to reduce the influence of mechanical losses during perturbation such as friction and "sloshing" of the working fluid medium inside of the sensors. By utilizing a small segment of electricity produced by the initial flow of the fluid within the device, the sensor mechanism has the capacity to utilize this electricity to trigger a counter-current which stops the flow of the fluid in the tube. In some cases, one can more accurately determine the actual amount of electrical current it takes to stop the flow of the fluid than one can accurately measure the direct flow of the fluid within the tube.
In the trade, velocity meters, accelerometers, and servo-motion sensors commonly find usage in such applications as geophones, seismometers, impact gauges, stethoscopes, inertial sensors as components of mutual guidance systems and various vehicle or vessel-steering or transverse-control systems, rotational motion measuring instruments, vibration measuring instruments, hydrophonic acoustical instruments, and other uses and applications. Servo-sensors are omni-positional and work in the absence of gravitational field, which makes them particularly useful in space.
Many of the sensors described above require some power source. Unfortunately, many applications for these sensors are in remote areas where no external power source is available. While batteries and the like can be used to power the device for a period of time, the period is clearly limited and requires replacement of the power source periodically to maintain the usefulness of the device.